Method for the recovery of process wastewaters of a fossil-fueled steam power plant and fossil-fueled steam power plant

ABSTRACT

A fossil-fueled steam power plant and method, the plant has a water-steam circuit, cooling water circuit, flue gas cleaning system and cooling tower. A fossil-fueled steam generator, steam turbine and condenser are connected to the water-steam circuit. In the cooling water circuit, a cooling tower and condenser are connected such that expanded steam is condensed by the exchange of heat with the cooling water circuit. The flue gas from the generator is cleaned in the flue gas cleaning system, and the cleaning system is supplied with process water. Process wastewater leaves the cleaning system. The cleaning system is connected to the cooling water circuit such that process water required for cleaning system is drawn from the cooling water circuit. To remove contaminated process wastewater, the cleaning system is connected to a wastewater treatment system having an evaporator, where system purified process wastewater is generated.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2014/067824 filed Aug. 21, 2014, and claims the benefitthereof. The International Application claims the benefit of GermanApplication No. DE 102013217335.0 filed Aug. 30, 2013. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to a steam power plant with cooling towerand flue gas purification plant and with a wastewater treatment plantfor process wastewater and in particular for recovering process water.The invention furthermore relates to a method for operating a steampower plant with cooling tower and flue gas purification plant.

BACKGROUND OF INVENTION

Steam power plants serve to generate electrical energy. A steam powerplant substantially comprises a fired boiler, a steam turbine, awater-steam circuit, a condenser, a cooling tower and a flue gaspurification plant.

The working medium used in the water-steam circuit in steam power plantsis deionized water which is produced in a deionization plant usingion-exchange resins. The deionized water is evaporated in the steamgenerator and passed into the steam turbine where it is expanded. Theenergy released during expansion is transferred via a shaft to thegenerator. The expanded steam is then fed to a condenser, and the liquidphase is condensed. To assist the condensation process, an evacuationsystem is connected to the condenser, which system produces a vacuum inthe condenser when the steam power plant is started up, and maintains itduring operation. The vacuum increases steam turbine efficiency andremoves non-condensable gases from the liquid stream.

During the energy generation process, various contaminants may beintroduced into the working medium. In addition, various substances areadded to the working medium for conditioning or purification.

The contaminants and additives in particular include ammonia, calcium,magnesium, sodium, potassium, chlorides, nitrates, sulfates (sulfuricacid) and silicon dioxide. The working medium contaminated bycontaminants or additives must be discharged from the water-steamcircuit as process wastewater, since the contaminants stand in the wayof direct reuse as a working medium in the water-steam circuit.

Ammonia serves as an alkalizing agent for conditioning the feed water.Through the addition of ammonia, an increase in the pH value of theworking medium may be achieved, whereby the relative corrosion rate ofthe feed water is reduced. Since the distribution coefficient of ammoniain liquids and steam is different, locally markedly elevated ammoniaconcentrations may occur in system parts involving evaporation andcondensation processes.

Process wastewaters arise at various points in the steam power plant. Alarge proportion of contaminated water arises in the form of thedesalination stream from the boiler drums in the evacuation system. Onstartup and shutdown, deficiencies (due to additional feeding of workingmedium) and excesses (due to discharge of working medium) of the workingmedium must be compensated. Moreover, process wastewaters arise due towater samples being taken and leaks in the water-steam circuit. As aresult of the above-stated water losses, the water-steam circuit must becontinuously additionally fed with deionized water (DIW). Backwashingand regeneration processes in the deionization plant and condensatepurification also result in process wastewaters.

Further process wastewaters arise through drainage. Drainage isperformed for example during ongoing operation from pipes in whichcondensate has collected and which have been closed for an extendedperiod. To this end, the pipes are opened briefly and thus drained.Water is then lost from the water circuit, which has to be replaced bymake-up water (DIW). Drainage also in particular arises to a greaterextent on startup and shutdown of the steam power plant, since forexample on shutdown of the steam power plant the steam in the watercircuit gradually condenses and the resultant liquid water must not beallowed to stand in the plant parts, in particular in the heatingsurfaces. On shutdown, more water is drained from the water circuit thanis replenished, until ultimately no more water is replenished.

According to the current prior art, the process wastewaters from thewater-steam circuit are, depending on quality, returned to thewater-steam circuit or discharged into the cooling tower or theindustrial wastewater system.

Further highly contaminated process wastewaters arise from the flue gaspurification plant, wherein large volumes of process wastewater with ahigh pollutant load arise from flue gas desulfurization in coal-firedsteam power plants. In steam power plants with a cooling tower, however,the majority of the process wastewater arises in the form of blowdownsfrom the cooling tower (cooling tower blowdown) in the open coolingwater circuit. Cooling tower blowdowns have in the past been dischargedinto public watercourses via a receiving stream.

An exemplary 2×1050 MW fossil fuel-fired steam power plant according tothe prior art with natural draft cooling tower and a wet limestone fluegas purification plant produces up to 100,000 tonnes of processwastewater per year in base-load operation, which has to be dischargedinto public watercourses. Just about half of this amount is accountedfor by the cooling tower.

Due to ever more stringent environmental legislation, and in thosecountries suffering water shortages, it is becoming increasinglyimportant to reduce water consumption and thus reuse wastewaters andprocess waters within the water-steam circuit. In particular, theguidelines for discharging wastewaters into public watercourses arebecoming ever more stringent. The water consumption of a steam powerplant should therefore be reduced as much as possible.

SUMMARY OF INVENTION

The object of the invention is therefore that of providing a steam powerplant in which the total water consumption of a steam power plant, thepollutant load in the remaining wastewater, in particular the wastewaterfrom the flue gas purification plant, and the consumption of deionizedwater are minimized. The object of the invention is furthermore that ofproviding a method for operating a steam power plant in which totalwater consumption is minimized.

The apparatus-related object of the invention is achieved by thefeatures in the independent apparatus claim.

The fossil fuel-fired steam power plant here comprises a water-steamcircuit, a cooling water circuit, a cooling tower and a flue gaspurification plant. A fossil fuel-fired steam generator, a steamturbine, and a condenser are connected into the cooling water circuit. Acooling tower and the condenser are interconnected in the cooling watercircuit in such a manner that expanded steam from the water-steamcircuit is condensable in the condenser by heat exchange with thecooling water circuit. The flue gas from the fossil fuel-fired steamgenerator may be purified, for example of carbon dioxide (CO₂), in theflue gas purification plant. To this end, process water may be suppliedto the flue gas purification plant and process wastewater may bedischarged therefrom. According to the invention, the flue gaspurification plant is connected to the cooling water circuit in such amanner that the process water required for flue gas purification may bedrawn from the cooling water circuit. In addition, the flue gaspurification plant is connected to a wastewater treatment plantcomprising an evaporator for discharge of process wastewater. Purifiedprocess wastewater may be produced by the wastewater treatment plant.

The invention is here based on the consideration, on the one hand, ofusing water from the cooling water circuit for flue gas purificationand, on the other hand, of purifying the process wastewater contaminatedby the flue gas purification by evaporation in the wastewater treatmentplant, so giving rise to cleaner process wastewater. As a consequence,the raw water requirement of the steam power plant may be reduced by theamount of the additional water requirement of the flue gas purificationplant.

As a result of lower water usage or optimized water treatment, theconsumption of chemicals may also be lowered, whereby the environmentalbalance of the power plant may be made more resource-efficient.

Various technologies are available for concentrating the wastewatersfrom flue gas desulfurization by evaporation. Theoretically, alldissolved constituents are removed from the wastewater by evaporationand crystallization. These constituents may then be disposed of as asolid. The distillate is of high purity and may be reused in the powerplant. It is possible to introduce the distillate into the raw watertank or into the permeate tank of the deionization plant. Thewastewaters with their high pollutant loads from flue gas purificationare completely processed by evaporation. The raw water requirement andthe wastewater volume of the power plant are thus reduced.

In a corresponding embodiment of the fossil fuel-fired steam powerplant, the flue gas purification plant is connected to the cooling watercircuit downstream of the cooling tower in such a manner that coolingtower blowdown water may be used as process water for flue gaspurification. Cooling tower blowdown is wastewater which necessarilyoccurs in large volumes as contaminated process water in a power stationwith a cooling tower and is thus always available. The total wastewatervolume is reduced as a consequence since the process water isadditionally concentrated in the flue gas purification plant.

Depending on local guidelines and specifications or prerequisites,concentration may however also be considered disadvantageous since theprocess wastewater is repeatedly concentrated in the flue gaspurification plant. The salt and heavy metal loading and the input ofpollutants by flue gas purification into the process wastewater mayreach very high levels as a consequence. An improved and particularembodiment of the fossil fuel-fired steam power plant therefore proposessupplying the flue gas purification plant with a process water which isconnected from the cooling water circuit upstream of the cooling towerand upstream of a cooling tower make-up water treatment plant. Saidprocess water has not yet been treated in the cooling tower make-upwater treatment plant and is thus untreated.

It is advantageous here that the water is in each case concentrated onlyonce in the flue gas purification plant and it is therefore easier tocomply with limit values for chloride, sulfate and heavy metals.Furthermore, the additional input of chloride into the processwastewater due to precipitation with FeCl₃ during cooling tower make-upwater treatment also does not occur. Since the cooling tower blowdown isnot put to any further use in this case, it can be more highlyconcentrated. The volume of make-up water for the cooling tower fallsbecause the level of blowdown is lower. As a consequence, the waterconsumption of the steam power plant is reduced. Depending on therequired purity of the gypsum arising in the cooling water circuitduring operation of the steam power plant (gypsum purity/degree ofwhiteness) and the quality of the raw water, any solids may however haveto be removed from the untreated cooling tower make-up water, forexample by a settling tank.

In a further alternative embodiment of the fossil fuel-fired steam powerplant, the flue gas purification plant is connected to the cooling watercircuit upstream of the cooling tower and to a cooling tower make-upwater treatment plant, such that cooling tower water treated for use inthe cooling tower may be used as process water for flue gaspurification. If treated cooling tower make-up water is used as processwater, said water is concentrated only once, whereby it is easier tocomply with limit values. As a result of precipitation with FeCl₃ in thecooling tower make-up water, the chloride content of the water isslightly raised. Since the cooling tower blowdown is not put to anyfurther use, it can be more highly concentrated. As a consequence, thevolume of make-up water for the cooling tower falls because the level ofblowdown is lower. As a consequence, the water consumption of the powerplant is reduced. This measure may also be necessary if the totaldischarge volume for wastewater into the receiving stream is fixed.

In one further development of the embodiment of the fossil fuel-firedsteam power plant, the wastewater treatment plant is connected to adeionization plant included in the water-steam circuit. As aconsequence, purified process wastewater from the wastewater treatmentplant may be introduced into the deionization plant. The purifiedprocess wastewater thus contributes to additionally feeding thewater-steam circuit, thereby on the one hand saving raw water foradditional feeding and on the other hand reducing the load on thedeionization plant since less deionized water (DIW) need be produced.

In an alternative further development of the embodiment of the fossilfuel-fired steam power plant, the wastewater treatment plant isconnected to a cooling tower make-up water treatment plant included inthe water-steam circuit. As a consequence, purified process wastewaterfrom the wastewater treatment plant may be introduced into the coolingtower make-up water treatment plant.

The wastewater treatment plant is advantageously furthermore alsoconnected to the condensate purification plant, the evacuation systemand sampling point for introduction of contaminated process wastewatersfrom the water-steam circuit into the wastewater treatment plant.

All the process wastewaters from the condensate purification plant arerecirculated into the water-steam circuit via the wastewater treatmentplant. The process wastewaters which arise during startup for boilerflushing are recovered as a consequence. Since boiler flushing isperformed with DIW, the discarded process wastewaters are of goodquality. The auxiliary boiler is likewise fed with DIW, for which reasonthe process wastewater (blowdown) is of high quality. The processwastewater from the auxiliary boiler must be expected to have elevatedion concentrations and to be contaminated with iron particles.

By recirculating the condensate arising in the wastewater treatmentplant by evaporation into the deionization plant, up to 75,200 tonnesper year less DIW have to be treated by the deionization plant in thesteam power plant mentioned by way of example. Around 15,000 tonnes peryear of this is accounted for by the recoverable process wastewatersfrom boiler flushing and startup, around 4,300 tonnes per year byrecoverable blowdowns from the auxiliary boiler, up to 6,000 tonnes peryear by process wastewater from the sampling point and around 50,000tonnes per year by condenser recovery.

The streams which may be recirculated into the water-steam circuitcomprise low levels of contaminants (for example iron particles andammonia). Before recirculation into the water-steam circuit, thesestreams must therefore be purified using the condensate purificationplant. This may proceed by feeding into the riser tube of the condenserupstream of the condensate purification plant. In the case ofrecirculation upstream of the condensate purification plant, the maximumoperating temperature of the ion exchangers in the condensatepurification plant must be borne in mind. Under certain circumstances,the recirculated streams must firstly be cooled. The service life of thecondensate purification plant is reduced by the higher ion loading. Thevolume of DIW which has to be provided by the deionization plant islower, since less make-up water is required.

The method-related object of the invention is achieved by the featuresof the independent method claim.

The method for operating a fossil fuel-fired steam power plant comprisesa steam power plant with a water-steam circuit, a cooling water circuit,a flue gas purification plant and a cooling tower. A fossil fuel-firedsteam generator, a steam turbine, and a condenser are connected into thewater-steam circuit, wherein steam is generated in the steam generator,and said steam is expanded in the steam turbine, and passed into thecondenser. A cooling tower and the condenser are interconnected in thecooling water circuit in such a manner that the expanded steam from thewater-steam circuit is condensed in the condenser by heat exchange withthe cooling water circuit. Flue gas from the fossil fuel-fired steamgenerator is purified in the flue gas purification plant. The processwater required for the flue gas purification plant is here drawn fromthe cooling water circuit. Said water is contaminated by flue gaspurification, wherein contaminated process wastewater is formed. Thecontaminated process wastewater is supplied to a wastewater treatmentplant comprising an evaporator, in which a purified process wastewateris formed by evaporation.

The advantages of the method according to the invention correspond tothose of the apparatus according to the invention.

In a corresponding embodiment of the method, the flue gas purificationplant is supplied with a cooling tower blowdown water as process waterwhich is drawn from the cooling water circuit downstream of the coolingtower.

In a particular embodiment of the method, the flue gas purificationplant is supplied with an as yet untreated cooling tower water asprocess water which is drawn from the cooling water circuit upstream ofthe cooling tower and upstream of a cooling tower make-up watertreatment plant.

In an alternative embodiment of the method, the flue gas purificationplant is supplied with a treated cooling tower water as process waterwhich is drawn from the cooling water circuit upstream of the coolingtower of a cooling tower make-up water treatment plant.

In a further development of the method, the purified process wastewateris passed out of the wastewater treatment plant into a deionizationplant included in the water-steam circuit.

In an alternative development of the method, the purified processwastewater is passed out of the wastewater treatment plant into acooling tower make-up water treatment plant included in the coolingwater circuit.

In another further development of the method, contaminated processwastewaters from the water-steam circuit, from the condensatepurification plant, from the evacuation system and the sampling pointare furthermore additionally introduced into the wastewater treatmentplant.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained below in greaterdetail with reference to figures in which:

FIG. 1 shows a fossil fuel-fired steam power plant with cooling towerand flue gas purification plant according to the prior art,

FIG. 2 shows a first embodiment of the fossil fuel-fired steam powerplant according to the invention with use of cooling tower blowdownwater as process water for flue gas purification,

FIG. 3 shows a second embodiment of the fossil fuel-fired steam powerplant according to the invention with use of untreated cooling towerwater as process water for flue gas purification,

FIG. 4 shows a third embodiment of the fossil fuel-fired steam powerplant according to the invention with use of treated cooling tower wateras process water for flue gas purification

FIG. 5 shows a fossil fuel-fired steam power plant with cooling towerand flue gas purification plant with process wastewater recovery.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 is a schematic diagram of a fossil fuel-fired steam power plant 1with cooling tower 7 and flue gas purification plant 8 according to theprior art. The fossil fuel-fired steam power plant 1 comprises a largelyclosed water-steam circuit 2 and an open cooling water circuit 6.

Raw water 25, for example from a public watercourse, is supplied to araw water tank 24 where it is held in intermediate storage. The rawwater 25 is conveyed from the raw water tank 24 into a cooling towermake-up water treatment plant 16. The raw water 25 is filtered andpurified in the cooling tower make-up water treatment plant 16.

Water from the cooling tower make-up water treatment plant 16 isdeionized for the water-steam circuit 2 in a deionization plant 19 usingion-exchange resins. A process wastewater 26 contaminated by reverseosmosis is passed via a receiving stream 27 back into the publicwatercourse. DIW 28 formed in the deionization plant 19 is supplied tothe water-steam circuit 2. In the water-steam circuit 2, the DIW 28 isevaporated in a fossil fuel-fired steam generator 3. The resultant steamis expanded in a steam turbine which is not explained in greater detail.

The expanded steam is then condensed in a condenser 5. In order toassist the condensation process, the water-steam circuit 2 comprises anevacuation system 21. The condensate is supplied to a condensatepurification plant 20 and subjected to mechanical purification. In orderto enable ongoing monitoring of water quality during operation of thesteam power plant 1, a sampling point 22 is provided from which watersamples may be taken on an ongoing basis from the water-steam circuit 2.Some of the water samples are here mixed with chemicals.

Slightly contaminated process wastewaters 30 and severely contaminatedprocess wastewaters 23 are discharged from the water-steam circuit 2.

The process wastewater 23 from the condensate purification plant 20 isparticularly highly contaminated and must be sent for external disposal.The highly contaminated process wastewaters 23 from the evacuationsystem 21, the highly contaminated samples from the sampling point 22,and the severely contaminated process wastewaters 23 arising fromflushing the steam generator 3 on startup of the steam generator 3 arepassed back into the raw water tank 24.

The slightly contaminated process wastewaters 30 from the auxiliarysteam generator 29 and the condensate formed on startup in the condenser5 are passed into the cooling tower 7. Recirculation of relatively cleancondensate from the condenser 5 into the steam generator 3 is not shown.

For the cooling water circuit 6, the water purified in the cooling towermake-up water treatment plant 16 is passed into the condenser 5 where itundergoes indirect heat exchange with the expanded steam. As a result,the steam condenses and the water in the cooling water circuit 6 isheated. The heated water from the cooling water circuit is supplied tothe cooling tower 7, where it is atomized and releases heat to theambient air by evaporation and convection with the air.

Cooled cooling water leaves the cooling tower 7 and is discharged viathe receiving stream 27 into the public watercourse.

Process water 9 for the flue gas purification plant 8 is also drawn fromthe cooling tower make-up water treatment plant 16. The process water 9contaminated in the flue gas purification plant 8 by input of flue gasresidues is likewise discharged into the receiving stream 27 as processwastewater 10.

FIGS. 2 to 4 each show inventive embodiments of the inventionrespectively having a raw water tank 24, a cooling tower make-up watertreatment plant 16, a cooling tower 7, a flue gas purification plant 8,a wastewater treatment plant 13 comprising an evaporator 12, and areceiving stream 27.

Raw water 25 from a public watercourse is supplied to the raw water tank24 and stored therein. From the raw water tank 24, the raw water 25 isthen passed into the cooling tower make-up water treatment plant 16where it is treated. The treated water thereafter undergoes heatexchange with the expanded steam in the condenser via the cooling watercircuit 6, but this is not explained in greater detail here. The coolingwater which is heated as a consequence is then supplied to the coolingtower 7. Cooled cooling tower blowdown water leaves the cooling towerand is discharged into the receiving stream 27.

FIG. 2 shows an inventive embodiment of the invention, wherein the fluegas purification plant 8 is supplied with the cooling tower blowdownwater as process water 9 which is drawn from the cooling water circuit 6downstream of the cooling tower 7. The contaminated process wastewater10 leaving the flue gas purification plant 8 is supplied to thewastewater treatment plant 13. The remaining cooling tower blowdownwater from the cooling tower 7 is passed into the receiving stream 27.

FIG. 3 shows a particular embodiment of the invention, wherein the fluegas purification plant 8 is supplied with an as yet untreated coolingtower water 17 as process water 9 which is drawn from the cooling watercircuit 6 upstream of the cooling tower 7 and upstream of a coolingtower make-up water treatment plant 16.

FIG. 4 shows a further alternative embodiment of the invention, whereinthe flue gas purification plant 8 is supplied with a treated coolingtower water 18 as process water 9 which is drawn from the cooling watercircuit 6 upstream of the cooling tower 7 of a cooling tower make-upwater treatment plant 16.

FIG. 5 shows a fossil fuel-fired steam power plant 1 with cooling tower7 and flue gas purification plant 8 with process wastewater recovery.

In contrast with the fossil fuel-fired steam power plant 1 according tothe prior art shown in FIG. 1, in this case a wastewater treatment plant13 is provided which, in addition to the contaminated processwastewaters from the cooling water circuit 11, also purifies theseverely contaminated process wastewaters from the water-steam circuit23.

The wastewater treatment plant 13 is accordingly supplied with thecontaminated process wastewater 10 from the flue gas purification plant8.

The wastewater treatment plant 13 is furthermore supplied with theseverely contaminated process wastewaters 23 from the water-steamcircuit 2, from the condensate purification plant 20, from theevacuation system 21, the sampling point 22, and the severelycontaminated process wastewaters 23 arising from flushing the steamgenerator 3 on startup of the steam generator 3. The wastewatertreatment plant 13 is furthermore supplied in a separate waste waterstream with the slightly contaminated process wastewaters 30 from thewater-steam circuit 2 and the condensate formed on startup in thecondenser 5. Recirculation of relatively clean condensate from thecondenser 5 into the steam generator 3 is not shown.

The contaminated process wastewaters are evaporated in the wastewatertreatment plant 13, wherein a condensate 32 and a solid 31 are formed.Depending on requirements or mode of operation, the condensate 32 isrecirculated either into the cooling tower make-up water treatment plant16 or into the deionization plant 19.

1. A fossil fuel-fired steam power plant, comprising a water-steamcircuit into which are connected a fossil fuel-fired steam generator, asteam turbine, and a condenser, a cooling water circuit, into which areconnected a cooling tower and the condenser, wherein expanded steam fromthe water-steam circuit is condensable in the condenser by heat exchangewith the cooling water circuit, and a flue gas purification plant, inwhich flue gas from the fossil fuel-fired steam generator is purified,wherein the flue gas purification plant is supplied with a process waterand a process wastewater is discharged therefrom, wherein the flue gaspurification plant is connected to the cooling water circuit, such thatthe process water required for the flue gas purification plant is drawnfrom the cooling water circuit, and the flue gas purification plant isconnected for discharge of contaminated process wastewater to awastewater treatment plant comprising an evaporator and by which apurified process wastewater is produced.
 2. The fossil fuel-fired steampower plant as claimed in claim 1, wherein the flue gas purificationplant is connected to the cooling water circuit downstream of thecooling tower, such that cooling tower blowdown water is used as processwater for the flue gas purification plant.
 3. The fossil fuel-firedsteam power plant as claimed in claim 1, wherein the flue gaspurification plant is connected to the cooling water circuit upstream ofthe cooling tower and upstream of a cooling tower make-up watertreatment plant, such that an as yet untreated cooling tower water foruse in the cooling tower is used as process water for the flue gaspurification plant.
 4. The fossil fuel-fired steam power plant asclaimed in claim 1, wherein the flue gas purification plant is connectedto the cooling water circuit upstream of the cooling tower and to acooling tower make-up water treatment plant, such that a cooling towerwater treated for use in the cooling tower is used as process water forthe flue gas purification plant.
 5. The fossil fuel-fired steam powerplant as claimed in claim 1, wherein the wastewater treatment plant isconnected to a deionization plant connected into the water-steamcircuit, such that a purified process wastewater from the wastewatertreatment plant is passed into the deionization plant.
 6. The fossilfuel-fired steam power plant as claimed in claim 1, wherein thewastewater treatment plant is connected to a cooling tower make-up watertreatment plant connected into the water-steam circuit, such that apurified process wastewater from the wastewater treatment plant ispassed into the cooling tower make-up water treatment plant.
 7. Thefossil fuel-fired steam power plant as claimed in claim 1, wherein thewastewater treatment plant is furthermore additionally connected to thecondensate purification plant, the evacuation system and the samplingpoint for introduction of contaminated process wastewaters from thewater-steam circuit into the wastewater treatment plant.
 8. A method foroperating a fossil fuel-fired steam power plant, comprising awater-steam circuit, into which are connected a fossil fuel-fired steamgenerator, a steam turbine, and a condenser, wherein steam is generatedin the steam generator, and said steam is expanded in the steam turbine,and passed into the condenser, a cooling water circuit, into which areconnected a cooling tower and the condenser, wherein the expanded steamfrom the water-steam circuit is condensed in the condenser by heatexchange with the cooling water circuit, and a flue gas purificationplant, in which flue gas from the fossil fuel-fired steam generator ispurified, the method comprising: drawing the process water required forthe flue gas purification plant from the cooling water circuit, whichwater is contaminated by flue gas purification, wherein contaminatedprocess wastewater is formed, and supplying the contaminated processwastewater to a wastewater treatment plant comprising an evaporator, inwhich a purified process wastewater is formed by evaporation.
 9. Themethod for operating a fossil fuel-fired steam power plant as claimed inclaim 8, wherein the flue gas purification plant is supplied with acooling tower blowdown water as process water which is drawn from thecooling water circuit downstream of the cooling tower.
 10. The methodfor operating a fossil fuel-fired steam power plant as claimed in claim8, wherein the flue gas purification plant is supplied with an as yetuntreated cooling tower water as process water which is drawn from thecooling water circuit upstream of the cooling tower and upstream of acooling tower make-up water treatment plant.
 11. The method foroperating a fossil fuel-fired steam power plant as claimed in claim 8,wherein the flue gas purification plant is supplied with a treatedcooling tower water as process water which is drawn from the coolingwater circuit upstream of the cooling tower of a cooling tower make-upwater treatment plant.
 12. The method for operating a fossil fuel-firedsteam power plant as claimed in claim 8, wherein the purified processwastewater from the wastewater treatment plant is passed into adeionization plant connected into the water-steam circuit.
 13. Themethod for operating a fossil fuel-fired steam power plant as claimed inclaim 8, wherein the purified process wastewater from the wastewatertreatment plant is passed into a cooling tower make-up water treatmentplant connected into the water-steam circuit.
 14. The method foroperating a fossil fuel-fired steam power plant as claimed in claim 8,wherein contaminated process wastewaters from the water-steam circuit,from the condensate purification plant, from the evacuation system andthe sampling point are furthermore additionally introduced into thewastewater treatment plant.